Prior to launch, spacecraft are regularly subjected to thermal vacuum testing to ensure that their payloads function as intended in the vacuum of space. Because the payloads of spacecraft frequently operate at very high power (e.g., radiating antennas operating at 2000 W or more), testing payload operations at full power in a vacuum environment presents a number of challenges. The power radiated from the antennas of the spacecraft must be fully absorbed, without any potentially damaging leakage of power reaching the receive antennas or any other flight hardware.
One approach to absorbing the power radiated by a spacecraft in a thermal vacuum (“TVAC”) chamber uses large and expensive absorber boxes that surround the power generating antennas. Because these absorber boxes are so large, they frequently prevent all antennas on a spacecraft from being tested at the same time. Accordingly, the TVAC chamber must be de-pressurized, the absorber boxes moved to different antennas on the spacecraft and the TVAC chamber re-pressurized before testing can continue. This approach is very slow, as the process of de-pressurizing and re-pressurizing the TVAC chamber and testing the spacecraft can take up to two or three months.
Another approach uses waveguides to redirect the power generated by the radiating antennas of a spacecraft outside of the TVAC chamber through radio frequency-transparent ceramic windows. To attach the waveguides, it is necessary to decouple the radiating horn antennas from the spacecraft, which can negatively affect the accuracy of the payload testing. Because waveguides are sensitive to the polarization of radiation, working best with linearly polarized radiation, there may be significant return loss (i.e., reflection of incident radiation) with antennas that emit elliptically polarized radiation. Moreover, the ceramic window through which the waveguide directs the radiation presents a danger of vacuum compromise, which can result in damage to the spacecraft.
Accordingly, there is a need for a way to perform high-power thermal vacuum testing of spacecraft payloads that is less expensive, less time-consuming, and insensitive to polarization, that does not require decoupling horn antennas from the spacecraft, and that can accommodate all of the antennas on the spacecraft in one test set-up.